The present invention relates to a pressure control device for a dual type hydraulic braking system of a vehicle, more particularly, to one which is capable of controlling the hydraulic pressure to the wheel cylinders in both fluid pressure circuits by utilizing one inertia valve.
It is customary in a hydraulic braking system for a vehicle to divide the whole circuit, connecting a master cylinder which produces the braking fluid pressure and wheel cylinders disposed on front- and rear wheels, into two mutually independent circuits, with the object of enhancing safety of vehicle driving.
It is also generally practiced to dispose an inertia valve, for the purpose of preventing a locking phenomenon (slipping of tyres on the ground with the wheels being in rotation-ceased condition) of both the front- and rear wheels at a moment of brake application, capable of controlling the pressure in the wheel cylinders on the rear wheels (hereinafter called rear wheel cylinder) such that the rising gradient of the pressure in the rear wheel cylinders may be milder than that in the master cylinder, when the deceleration rate of the vehicle exceeds a certain predetermined value.
The inertia valve is characterized in the capability of controlling the braking pressure due to the deceleration of a vehicle per se, but it is defective in having a large fluctutation or ununiformity of the pressure controlled. Consequently, when the both circuits are respectively provided with an individual inertia valve, the braking force acted on each rear wheel may sometimes be imbalance, causing a resultant unfavorable halting of the vehicle. The present invention was made from such a background.